This invention relates to optical interconnection apparatus (optical circuit board) for mutually connecting optical component, parts and/or devices used in optical communications or optical information processing, such as optical components, optical circuit packs and optical circuit devices, and also to fabrication process thereof.
To permit optical interconnections between plural optical components in an optical circuit pack or optical interconnections between plural optical circuit packs or between optical circuit devices on each of which optical packs are mounted, these optical components, optical circuit packs and optical circuit devices are provided at terminals thereof with optical connectors to interconnect them together via optical fibers. As these optical fibers have to be arranged with loose in this case, it is a current circumstance that, on an optical circuit pack or inside and/or on a back side of an optical circuit devices, intricately routed lines of the optical fibers extend overlapping one another in the form of a bird""s nest and hence occupy a large space. For an optical interconnection process which is complex and requires a large space as described above, a proposal has been made, as a simple process anywhere routing of optical fibers on a two-dimensional plane as desired, to use a sheet or substrate with a pressure-sensitive adhesive coated thereon and to hold optical fibers in place by the pressure-sensitive adhesive as disclosed in JP 2,574,611 B.
Incidentally, the optical interconnection apparatus disclosed in JP 2,574,611 B is obtained in such a way that upon its fabrication, optical fibers are located by a pressure-sensitive adhesive, which is coated on a 25-200 xcexcm thick, flexible polymer film substrate (base layer) made of xe2x80x9cMylarxe2x80x9d or xe2x80x9cKaptonxe2x80x9d or on fiber jackets, to form a routing pattern and the routing pattern is then covered with the same material as the material used for the substrate, whereby a protective layer is formed. This process is however accompanied by problems in that as optical fibers so located increase in number and the optical fibers increase more overlapped portions (cross-over routing) in the routing pattern so formed, the resulting routing layer of the optical fibers becomes thicker and, because the tacky surface with which the optical fibers are in contact becomes smaller at the overlapped portions of the optical fibers, the protective layer cannot be arranged evenly. There is a further problem in that at the overlapped portions of the optical fibers in the routing pattern, the fixing force by the pressure-sensitive adhesive becomes weaker and the optical fibers are allowed to move, thereby resulting in displacements in the routing pattern (a loss in the intactness of the routing pattern). Moreover, general optical fibers range from 125 to 250 xcexcm in diameter so that at an overlapped area of three optical fibers, for example, the routing layer of the optical fibers becomes as thick as 375 to 750 xcexcm. An increase in the overlapped portions of optical fibers in a routing pattern develops lifted portions (air pockets) in a protective layer around optical fibers underneath the protective layer, so that a problem arises in the reliability against temperatures and humidities and in addition, the optical circuit board becomes extremely weak to breakage which may be caused by deformation such as bending. Moreover, the optical interconnection apparatus fabricated by this process includes polymer substrates, which do not have stretchability despite their flexibility, above and below a layer formed of the optical fibers and the pressure-sensitive adhesive and having a thickness of from several hundreds micrometers to several millimeters, and is thus accompanied by a still further problem that the optical interconnection apparatus is provided with reduced flexibility despite the need for high flexibility. The optical interconnection apparatus disclosed in Japanese Patent No. 2,574,611 B is provided at portions thereof, which are adapted for interconnections, with extended tabs. Extension of these tabs, however, results in the occupation of a greater space by the interconnecting portions and also leads to complication in the fabrication of the optical interconnection apparatus.
On the other hand, U.S. Pat. No. 5,292,390 discloses a process for filling a layer of routed optical fibers with a thermoplastic polyurethane to hold the optical fibers in place and also to protect the optical fibers. The problem of a reduction in flexibility, however, remains still unresolved in this process because xe2x80x9cKaptonxe2x80x9d films, which have low stretchability although their flexibility is high, are used as a substrate for an adhesive layer and a substrate for a thermoplastic polyurethane layer, said layers serving to hold the optical fibers in place, and the layer routing optical fibers also remain held between these films after the fabrication of an optical interconnection apparatus. Further, the polyurethane layer has stiffness despite its flexibility and therefore, stress tends to be applied to optical fibers held in place and protected by it and tends to result in an optical loss. There is accordingly a problem in protecting the optical fibers and holding them in place.
JP 10-68853 A, on the other hand, discloses to fabricate an optical interconnection apparatus by locating optical fibers between laminates, in each of which a film substrate and an adhesive layer are provided with a layer having compressibility, and holding the resulting optical fiber routing layer between the laminate. The layers having compressibility in that invention, however, are arranged to reduce pressures which may be applied to the optical fibers during the fabrication of the optical interconnection apparatus. The film substrates remain in the laminate layers between which the routed optical fibers are held on both sides. The problem of a reduction in the flexibility of an optical interconnection apparatus, therefore, remains still unresolved. Further, as a material which makes up the layers having compressibility, polytetrafluoroethylene, polyethylene, polyurethane foam or the like is used. Since these materials still retain stiffness despite their thermoplastic property, a problem exists in the protection and holding of optical fibers as in the patent referred to in the above.
As has been described above, the conventional optical interconnection apparatus with optical fibers located or routed by making use of flexible substrates is provided on both sides of the two-dimensionally routed optical fibers with film substrates of xe2x80x9cMylarxe2x80x9d or xe2x80x9cKaptonxe2x80x9d. Therefore, such film substrates are arranged on both sides of the optical fiber routing layer of several hundreds micrometers to several millimeters in thickness, and are exposed as surface layers. This optical fiber routing part hence has substantially reduced flexibility, and for optical interconnections, arrangement of extended tabs is needed. As adhesive layers include only on both sides of several hundreds micrometers to several millimeters, there is a problem in the fixed placement and protection of optical fibers. The optical fibers tend to loose the intactness of their pattern, resulting in a substantial optical loss. Therefore it cannot be used as an optical interconnection apparatus. When there is not much space for the arrangement of the optical interconnection apparatus upon interconnection of optical components themselves on an optical circuit pack or interconnection of optical circuit packs together, the optical interconnection apparatus cannot be used due to insufficient flexibility and bendability.
To connect and accommodate a number of optical fibers within a limited space, an optical interconnection apparatus such as an optical circuit board is an effective and indispensable part. A further increase in the number of optical fibers to be routed makes it difficult to route and accommodate all the optical fibers on one plane of a substrate because, if one attempts to route and accommodate such a greater number of optical fibers on the one plane of the substrate, the optical fibers so routed overlap one another to include more overlapped portions of the optical fibers themselves and the area of contact with a pressure-sensitive adhesive, which serves to locate the optical fibers and hold them in place, is decreased at the overlapped portions so that the routing cannot be achieved with good positional accuracy. Further, the routing and accommodation of a greater number of optical fibers on a single plane leads to an increase in the density of end portions which are arranged at their opposite ends for permitting optical interconnections, and hence, a problem arises in that a space required to plug into connectors and the like cannot be retained physically. To resolve these problems, stacking of substrates each of which carries optical fibers routed thereon is effective. This stacking, however involves a problem that flexibility is lost. It is accordingly the current circumstance that a multilayered optical circuit board equipped with flexibility required as an optical circuit board is still unavailable. JP 10-68853 referred to in the above discloses an example in which optical fibers are routed on both sides of a laminate which is provided with a layer having compressibility. However, this layer is arranged to reduce pressures which may be applied to the optical fibers, and is not intended to permit routing and accommodation of a greater number of optical fibers.
The present invention has been completed with a view to resolving various problems of the conventional art such as those described above. Described specifically, an object of the present invention is to provide an optical interconnection apparatus which makes it possible to readily interconnect optical units such as optical components, optical circuit packs and optical circuit devices and which is provided with at least one protective resin layer having high flexibility and/or good flexibility and enabling routing and accommodation of a number of optical fibers to keep the fixed and protected optical fibers unstressed, and also a fabrication process for the optical interconnection apparatus. Another object of the present invention is to provide a novel optical interconnection apparatus which permits ready optical interconnections to optical fibers routed in an overlapped fashion as described. A further object of the present invention is to provide a process for the fabrication of an optical interconnection apparatus, which makes it possible to economically form with a good yield at least one protective resin layer, which serves to hold routed optical fibers in place and protect them from external forces (pulling, bending, scratching, and the like), without losing the intactness of the routing pattern of the located optical fibers.
An optical interconnection apparatus according to a first embodiment of the present invention has a single substrate, and is characterized in that it comprises a substrate having a two-dimensional plane, a protective resin layer arranged on at least one side of the substrate and having flexibility, and plural optical fibers routed on the at least one side of the substrate and provided at opposite ends thereof with end portions adapted to permit optical interconnections thereto, and the routed optical fibers are held in place by the protective resin layer.
An optical interconnection apparatus according to a second embodiment of the present invention has two or more substrates, and is characterized in that the optical interconnection apparatus comprises at least two base films having two-dimensional planes, protective resin layers having flexibility and arranged on the respective base films and between base films, respectively, plural optical fibers routed on at least one sides of the respective base films and provided at opposite ends thereof with end portions adapted to permit optical interconnections thereto, the routed optical fibers are held in place by associated ones of the protective resin layers, respectively, and the respective base films are sandwiched by the protective resin layers, whereby a stacked structure is formed. As a preferred example of the optical interconnection apparatus according to the second embodiment, there is an optical interconnection apparatus comprising at least two base films having two-dimensional planes, protective resin layers having flexibility and arranged on the respective base films and between the base films, respectively, plural optical fibers routed on at least one sides of the respective base films and provided at opposite ends thereof with end portions adapted to permit optical interconnections thereto, said routed optical fibers being held in place by associated ones of the protective resin layers, respectively, and said respective base films being sandwiched by the protective resin layers, whereby a stacked structure is formed.
An optical interconnection apparatus according to a third embodiment of the present invention does not have a substrate, and is characterized in that it comprises plural optical fibers routed in a two-dimensional plane and provided at ends thereof with end portions adapted to permit optical interconnections and one or plural protective resin layers having flexibility, and the optical fibers are held in place in a form embedded in at least one of the protective resin layers. As a preferred example of the optical interconnection apparatus according to the third embodiment, there is an optical interconnection apparatus comprising plural optical fibers routed in a two-dimensional plane and provided at ends thereof with end portions adapted to permit optical interconnections and two or more protective resin layers stacked one over the other via an adhesive layer and having flexibility, said optical fibers being held in place in a form embedded in at least one of the two or more protective resin layers.
In the present invention, the optical interconnection apparatus of the first embodiment having a single substrate can be fabricated by routing plural optical fibers on one of sides of a substrate having a two-dimensional plane, for example, a flexible base film such that the optical fibers are provided at opposite ends thereof with end portions to be adapted to permit optical interconnections, and then forming a protective resin layer having flexibility such that the optical fibers so routed are held in place. Concerning the optical interconnection apparatus according to the first embodiment, a second protective resin layer having flexibility and made of the same or different resin material as or from that of the first protective resin layer may also be formed after the first protective resin layer is formed as described above. As an alternative, an optical interconnection apparatus can also be fabricated by routing, subsequent to the formation of the first protective resin layer as described above, plural optical fibers on the other side of the base film such that the optical fibers are provided at opposite ends thereof with end portions to be adapted to permit optical interconnections, and then forming a second protective resin layer, which has flexibility and is made of the same or different resin material as or from that of the first protective resin layer, such that the optical fibers so routed are held in place.
In the present invention, an optical interconnection apparatus having two or more base films can be fabricated by a process which comprises stacking a flexible base film having a two-dimensional plane by adhesion or the like over one of protective resin layers of an optical interconnection apparatus fabricated as described above, routing plural optical fibers on the base film such that the optical fibers are provided at opposite ends thereof with end portions to be adapted to permit optical interconnections, and then forming a third protective resin layer having flexibility such that the optical fibers so routed are held in place, whereby a stacked structure is fabricated. An optical interconnection apparatus which includes many base films with optical fibers routed thereon can be fabricated by repeating the step, in which the third protective resin layer is formed, to form a stacked structure of the plural base films and the plural protective resin layers with the corresponding optical fibers held in place therein.
In addition, an optical interconnection apparatus which includes plural base films can also be fabricated by adhering together protective resin layers of optical interconnection apparatus, each of which has been fabricated as described above and includes a single base film, such that a stacked structure is formed.
Upon fabrication of the optical interconnection apparatus according to the first or second embodiments of the present invention, it is preferable to form the protective resin layer by arranging an edge-dam member along or in a vicinity of a peripheral edge of the base film, filling a resin material inside the edge-dam member to form a protective resin layer, and then solidifying the resin material.
In the present invention, a first process for the fabrication of the film-less optical interconnection apparatus of the third embodiment is characterized in that the process comprises providing a stacked structure, which comprises a protective resin layer having flexibility and an adhesive layer, routing plural optical fibers on the adhesive layer such that the optical fibers are provided at opposite ends thereof with end portions to be adapted to permit optical interconnections, and then forming on the optical fibers another protective resin layer, which has flexibility and is made of the same or different resin material as that of the protective resin layer, to hold the optical fibers in place. The stacked structure may be fabricated by forming an adhesive layer on a protective resin layer, which has flexibility and has been obtained by forming the protective resin layer over a release film having a two-dimensional plane and then removing the film.
Further, a second process for the fabrication of the film-less optical interconnection apparatus of the third embodiment is characterized in that the process comprises providing as a temporary base film an adhesive base film having a two-dimensional release plane on which an adhesive layer is located, routing plural optical fibers on the adhesive layer such that the optical fibers are provided at opposite ends thereof with end portions to be adapted to permit optical interconnections, forming a first protective resin layer having flexibility on the routed optical fibers to hold the optical fibers in place, removing the release film on a back side, and then forming over the thus-exposed adhesive layer a second protective resin layer having flexibility and made of the same or different resin material as that of the protective resin layer.
In the second fabrication process, the optical interconnection apparatus can also be fabricated by forming a first protective resin layer to hold the optical fibers in place, removing the release film on a back side, routing on the thus-exposed adhesive layer other plural optical fibers such that the optical fibers are provided at opposite ends thereof with end portions to be adapted to permit optical interconnections, and then forming on the routed optical fibers a second protective resin layer having flexibility and made of the same or different resin material as that of the first protective resin layer to hold the optical fibers in place.
In the fabrication of the optical interconnection apparatus according to the third embodiment, the protective resin layer or the other protective resin layer can be formed by arranging an edge-dam member along or in a vicinity of a peripheral edge of the protective resin layer or the release film having the two-dimensional plane, filling a resin material inside the edge-dam member, and then solidifying the fixing resin layer.